There are three ways to tell if your skis need tuning: You can look at them, feel the edges and bases or simply ski on them. If the edges are rusty and pockmarked, they need to be cleaned up and sharpened. If the bases have gouges or scratches, these need to be filled and smoothed. If the bases show white, dried-out areas, they need wax.
A very sharp edge feels smooth. Test for sharpness with your fingernail, scraping it across the edge at 90 degrees. If you peel away a curl of fingernail the edge is sharp. Often, though, even if it feels sharp, it might not be. Instead, this "sharpness" may indicate the edge has a burr¿a coarse ridge of steel along the edge too fine to see. If it feels rough, as if it has saw teeth, you have dings and nicks that must be removed with a file or whetstone.
On the snow, untuned skis feel sticky and hard to turn. They also don't track in a straight line or hold on icy snow. Have them ground and sharpened (cost: about $30). Ideally, you should have this done after every 10 days of skiing. (If conditions are icy or rocky, you may need to do this more frequently.)
But beware: A poorly tuned ski is as bad as an untuned ski. It will grab or hook, jerking you through turns by constantly gripping, then releasing. If you're experiencing such jerkiness, your skis' edges might simply be too sharp. They will improve as the edges dull, but waiting until they dull is frustrating. Take them back to the shop, and ask the tech to dull the edges with emery paper or a gummy stone. Even when a ski is perfectly tuned, some skiers use a stone to dull the edges a few centimeters from the tip and tail. Here's why: Tips that are too sharp yank the ski into the turn too suddenly, resulting in a wobbly turn. Tails that are too sharp get hung up and run too straight out of the turn. The tips of the skis, in other words, are always fighting the tails.
Learning how your skis should feel will help you ski better. If you ski one resort regularly, buy a season tuning pass at a local shop. It's surprisingly cheap. Then, drop your skis off any time, and pick them up next time you ski. It's that easy.
Have a question for SKI's Instruction Editor Stu Campbell? Contact him at firstname.lastname@example.org.